docs: def checkTimestamp(nonce_string, allowed_skew=SKEW, now=None):
      """Is the timestamp that is part of the specified nonce string
      within the allowed clock-skew of the current time?
  
      @param nonce_string: The nonce that is being checked
      @type nonce_string: str
  
      @param allowed_skew: How many seconds should be allowed for
          completing the request, allowing for clock skew.
      @type allowed_skew: int
  
      @param now: The current time, as a Unix timestamp
      @type now: int
  
      @returntype: bool
      @returns: Whether the timestamp is correctly formatted and within
          the allowed skew of the current time.
      """
      try:
          stamp, _ = split(nonce_string)
      except ValueError:
          return False
      else:
          if now is None:
              now = time()
  
          # Time after which we should not use the nonce
          past = now - allowed_skew
  
          # Time that is too far in the future for us to allow
          future = now + allowed_skew
  
          # the stamp is not too far in the future and is not too far in
          # the past
          return past <= stamp <= future